feat: add Aforge benchmark runtime

[AbirAbbas]

Summary

• adds aforge as a first-class SWE-AF runtime (including aforge-v2 aliases)
• maps every planner/coder/reviewer role through the same AgentField Aforge adapter
• gives Aforge the same OpenRouter model defaults as the existing open runtime
• documents a source-build benchmark path and AFORGE_BIN override
• pins the exact AgentField harness commit from feat(harness): add Aforge parity across Python, Go, and TypeScript agentfield#905 for reproducible pre-release benchmarks

Coordinated with Agent-Field/aforge-v2#3 and Agent-Field/agentfield#905. Replace the source SDK pin with a released version before merge.

Verification

• AGENTFIELD_SERVER=http://localhost:9999 pytest tests/test_model_config.py tests/test_runtime_provider_routing.py -q (67 passed)
• dependency install from the pinned AgentField commit
• python -m compileall -q swe_af

The current Docker image does not bundle unreleased Aforge; host/source benchmarks work with AFORGE_BIN today.